1. Field of the Invention
The present invention relates to a method of driving a gas discharge display apparatus and the apparatus. The gas discharge display apparatus comprises a plurality of light-emitting tubes which are aligned and adhered to sheets having electrodes thereon, where each of the tubes forms a discharge space and includes a discharge gas and fluorescent material therein. The invention more particularly relates to the method of driving the apparatus which applies a voltage between a displaying electrode and an address electrode, both of which are orthogonally opposed each other via the discharge space, for making the fluorescent material emit light, and the apparatus.
2. Description of the Related Art
A display apparatus using gas discharge tubes, as one of the gas discharge display apparatus, is disclosed in the Japanese publication of unexamined application 2003-203603. The gas discharge tube has the structure in which a fluorescent material and a discharge gas are disposed or confined in a grass tube of a small diameter, and then a plurality of the tubes are aligned to form a display panel. Therefore, the large size display with the tubes has characterized in less process for assembling the display, smaller weight, and easiness for assembling for various sizes of screen.
In the display apparatus described above, a triple-electrode surface-discharge structure is adopted. That is, a plurality of the pairs of display electrodes are formed on an inner surface of a front substrate in such a direction as to be orthogonal to the longitudinal direction of the gas discharge tube at every scanning line of matrix display, for yielding a discharge in the tube. A plurality of address electrodes are provided on an inner surface of a rear substrate so as to intersect orthogonally to the display electrode pairs.
In the display apparatus described above using the gas discharge tubes, the pair of the display electrodes and the address electrode define the light-emitting region (also referred to as a cell hereinafter) from which light is emitted. Since the intensity of the light is defined the single discharge between the pair of display electrodes (also the discharge between the sustaining electrodes is referred to as sustaining discharge, and the display electrode also is referred to as the sustaining electrode), the intensity of light emitted from the fluorescent materiel in the cell is fixed. Since the intensity of light caused by single discharge is fixed, the method to perform the gray-scale display is explained with FIG. 1 which shows the structure of one field in display. In the case of displaying an image with 256-level gray-scale, for example, a screen (one field) is composed of several fields 600, and the field 600 is divided into eight subfields sf. Each subfield is composed of a reset period, an address period, and a sustaining period. The reset period is a period for erasing the wall charge for exerting the charge state in each of cells to the same state to avoid the effect of lighting in the previous sustaining period. The address period is a period for selecting a cell to be lit by addressing discharge (also referred to as an opposed discharge) between an address electrode and one of the pair of display electrodes corresponding to the cell, then the charge is accumulated at a portion of the tube close to the display electrode served in the opposed discharge. And for a gray-scale display, the ratio of the number of discharges between a pair of display electrodes for lighting during a sustaining period in each subfield is set as 1:2:4:8:16:32:64:128 so as to realize the relative ratio of brightness as 1:2:4:8:16:32:84:128. That is, the each subfield is a period in which an image of a gray-scale level is displayed.
FIG. 2 shows details of the sustaining period shown in FIG. 1. The waveforms of pulses applied to the sustaining electrodes X and Y shown in FIG. 2 are conventionally used during the sustaining period. The waves shows example of waveforms of voltage applied to the address electrode A, the sustaining electrodes X or Y, respectively, where the sustaining electrodes X and Y compose a pair of display electrode. At the timing the pulse 660 being applied to the sustaining electrode X, the positive wall charge has been accumulated on the dielectric member, such as the grace glass of tube, close to the sustaining electrode X, while the negative wall charge has been accumulated on the dielectric member close to the sustaining electrode Y. Then the actual applied voltage on the sustaining electrode X is sum of voltage by the pulse 660 and the wall charge close to the electrode X when the pulse 660 is applied to the sustaining electrode X, while the actual voltage of the sustaining electrode Y is negative because of negative wall charge close to the sustaining electrode Y. Therefore, a voltage higher than the value of the pulse 660 is applied between the sustaining electrodes X and Y, and then the sustaining discharge is initiated between them. After this sustaining discharge, the negative wall charge is accumulated on the portion close to the sustaining electrode X and positive wall charge is accumulated on the portion close to the sustaining electrode Y. And then when the pulse 670 is applied to the sustaining electrode Y, the sustaining discharge is generated between the sustaining electrodes X and Y. Thus at each when time pulses 662, 672, 664, 674, 666, 676 are alternatively applied to the respective sustaining electrodes X or Y, the sustaining discharge is generated. The discharge generates the ultraviolet rays which make the fluorescent material glow in turn. As described above, the gas discharge display apparatus of the triple-electrode surface-discharge type performs a gray scale display with varying the number of sustaining discharges between the pair of display electrodes. However, the brightness to be displayed is limited to integral multiple of a brightness caused by single sustaining discharge. Therefore the conventional gas discharge display apparatus can perform the gray-scale display which is limited within the integral multiple of the gray-scale display level corresponding to the brightness caused by the single sustaining discharge. That is, the realization of a continuously smooth gray-scale display level is difficult for the conventional gas discharge display apparatus.